The present invention is related generally to electrical power systems, and in particular to starting/generating systems.
Starting/generating systems refer to systems capable of operating in either a starting mode in which the system operates as a motor to accelerate a rotor portion to a desired speed or in a generating mode in which the system operates as a generator to convert mechanical energy provided by the rotor portion into electrical energy for distribution to attached loads.
Depending on the mode, various electronic circuits are required to provide the desired functionality. During starting, a pre-charging or soft-start circuit may be employed to prevent large in-rush currents from damaging a DC link capacitor(s). For example, prior art pre-charge circuits may employ a switching device and resistor (connected in parallel with one another) connected in series on the DC link bus between the power supply and the inverter/rectifier circuit. The switching device is turned OFF in order to force current through the resistor connected in parallel with the switching device, thereby limiting the current provided to the inverter/rectifier circuit and DC link capacitor. However, this topology does not provide functionality beyond pre-charge operations. Alternatively, the switching device and resistor can be placed in series with the DC link capacitor, which is connected between the DC link buses in parallel with the inverter/rectifier circuit. In this way, the switching device is not required to be capable of carrying the full inverter/rectifier current, but the presence of the switching device in series with the capacitor decreases the performance of the DC link capacitor, due to the resistance of the switching device.
In addition to circuits or components employed to provide pre-charging functionality, starting/generating systems employ additional hardware/circuits to implement functions such as battery charging, power flow enablement, and fault protection. These additional hardware/circuit components add to the overall cost and weight of starting/generating systems, reduction of which is desirable.